1. Field of the Invention
The present invention relates generally to conductive gaskets for shielding against electromagnetic interference (EMI gaskets), and more particularly, to a conductive gasket having improved performance when providing contact through non-conductive coatings.
2. Background Information
Conductive gaskets are widely used to prevent electromagnetic interference (EMI) leakage and entrance into and from electronic equipment. In particular, EMI gaskets are provided at the interfaces of computer cabinets and cabinets containing other electronic equipment so that radiated emissions fall below maximum radiated emissions requirements of various authorities such as the U.S. Federal Communications Commission (FCC) standards and Canadian Standards Association (CSA).
Typically, a wire mesh gasket including an internal foam material is provided on flanges and other interfaces of cabinets having exposed conductive surfaces. When the cabinet is closed, the gaskets are compressed providing a low-impedance contact between cabinet portions via the conductive wire mesh.
However, non-conductive coatings such as organic anti-fingerprint coatings are often used on equipment surfaces in order to provide improved appearance and to avoid oxidation initiated by contact with acids transferred from human skin. In addition, such coatings prevent oxidation occurring naturally on exposed metal surfaces that do not have anti-corrosion platings. When a gasket, or the surface that a gasket is to contact is coated with such a material, the surface conductivity may be dramatically reduced, requiring removal of the coating before a sufficiently low-impedance contact may be made with the gasket.
Also, in general, as frequencies of electronic equipment (in particular digital computing systems) continue to increase, improved shielding is necessary, and therefore the performance of conductive gaskets becomes more critical.
Therefore, it would be desirable to provide a conductive gasket and method of manufacture for a conductive gasket having improved performance, and in particular a conductive gasket that will operate reliably when either the gasket or a mating surface is coated with a non-conductive coating.
The objective of providing improved conductive gasket performance, particularly in the presence of non-conductive coatings, is accomplished in a new conductive gasket and method of manufacture.
The gasket includes a contact strip provided beneath a flexible conductive cover. The cover may be a conductive wire mesh, or alternatively, a flexible plastic with a conductive coating on an exterior surface. The contact strip includes multiple protrusions that may pass through the cover when the gasket is compressed, providing improved contact with the surface that the protrusions contact and penetration of any non-conductive coating that is present. Holes may also be provided in a flexible plastic cover so that protrusions may pass through without damaging the cover.
Alternatively, the protrusions may be relatively smooth projections or bends in the contact strip that cause the flexible cover to bend sharply, providing corners in the cover that will break through any non-conductive coating that is present. The gasket may include a foam insert to restore the shape of the gasket when a compressive force is removed. A foam section may be included above the protrusions in order to preserve the shape of the gasket. Or, the gasket may be made entirely from a wire mesh with a contact strip woven inside. The contact strip may include protrusions on both faces so that contact is enhanced with two surfaces when the gasket is compressed.
The foregoing and other objectives, features, and advantages of the invention will be apparent from the following, more particular, description of the preferred embodiment of the invention, as illustrated in the accompanying drawings.